The present invention relates to signal lamps, e.g., to pilot lamps which can indicate the condition of one or more electric switches or the like. More particularly, the invention relates to improvements in pilot lamps or signal lamps (hereinafter called signal lamps) which are intended or are likely to be utilized under circumstances where water or another liquid tends to penetrate into their interior and, in the absence of appropriate precautionary measures, interfere with proper operation of the lamp by short-circuiting the conductor means connecting the light source or sources with a source of electrical energy.
It is already known to provide a signal lamp with a depressible actuator for one or more switches. The actuator has a tubular section which can cooperate with a mobile switching member in the interior of a housing member. A membrane is interposed between the housing member and the tubular section of the actuator to prevent penetration of liquids or solid contaminants into the interior of the lamp, especially into the space or spaces accommodating the electric conductor means. Reference may be had, for example, to German Offenlegungsschrift No. 29 14 709 which discloses a signal lamp of the just outlined character. The tubular section of the actuator has a cylindrical external surface which is form-lockingly engaged by the inner marginal portion of the membrane. The outer marginal portion of the membrane is caused to sealingly surround and to thus form-lockingly engage a clamping ring. Once the actuator is inserted into the housing member, the clamping ring urges the outer marginal portion of the membrane against a portion of the housing member. The external surface of the tubular section of the actuator has projections which serve to push the clamping ring into the housing member during insertion of the actuator, and to extract the clamping ring from the housing member in response to separation of the tubular section from the switching member.
A drawback of the just discussed conventional signal lamp is that the clamping ring and the outer marginal portion of the membrane are detachable from the housing member, i.e., that such parts become fully separated from the housing member when the actuator is extracted for the purpose of gaining access to the light source or for any other reason. The detached membrane is likely to be contaminated and/or damaged while the tubular section of the actuator is separated from the switching member.